1. Field of the Invention
This invention relates to structures and methods for fabricating thin film magnetic read and write heads. More specifically, the invention relates to structures and methods for fabricating a thin film recording head having reduced sensitivity to electrical breakdown resulting from electrostatic discharge from media surfaces.
2. Description of the Related Art
The extremely small dimensions of structures comprising the read and write components of today's hard disk drive thin film magnetic heads makes these heads susceptible to damage by electrostatic discharge sources. One important source is the disk media itself, where static charge potentials on the order of a few volts can damage a thin film head and the media surface if a voltage breakdown or electrical discharge occurs between the head and disk media. As fly heights decrease in response to demands for increased areal densities, a catastrophic discharge becomes more likely. The onrush of current produced by a discharge can damage both the sensitive thin film read devices as well as write devices in both longitudinal and perpendicular thin film heads. This problem is further exacerbated in heads having thermal fly height control (TFC), since the physical distortion of the thin film head produced during heating tends to extend the critical read and write structures toward the media disk, making them closer than the slider body and the nearest “lightening rods”.
Disclosure in the art have suggested a number of potential solutions to solve this problem. In some cases, semi-conductive layers embedded in the thin film heads have been proposed. These layers, however, are typically flush with the air bearing surface, along with other layers such as magnetic pole layers and shield layers. They are therefore ineffective in draining charge from a media surface, as the discharge will more likely be attracted to the metallic pole layers or shield layers. If this occurs, device damage will occur with or without the semi-conductive layers. Other references have suggested the use of a coating applied over the ABS. The problem with this technique is that the coating impacts the very critical head to surface dimensions which are on the order of 5 to 10 nm currently, and may drop to a few nanometers in the future. Thus, the thin coating itself will breakdown, resulting in a damaging current discharge. It is also difficult to reliably produce coatings on the order of a few nanometers that can carry the required current without being damaged themselves. What is needed is a better method to protect thin film magnetic heads from voltage breakdown.
FIG. 1 (Prior Art) is a partial cross sectional view 100 of a typical thin film longitudinal head, wherein the write head comprises write gap 112 bounded by upper 110 and lower 108 pole tips. Upper pole tip 110 is in contact with upper return pole layer 114. Lower pole tip 108 is in contact with lower return pole layer 106. Lower return pole layer is separated from shield layer 102 by insulating layer 104. The coil is shown as structure 116, embedded in insulating layer 118, which may also be referred to as an overcoat layer. The read head comprises a MR (magneto-resistive) sensor 103 located between upper 102 and lower 101 shield layers. Shield layer 101 is supported by undercoat layer 120 and an AlTiC base layer 122.
FIG. 2 (Prior Art) is a partial, cross sectional view 200 of a typical thin film perpendicular head. The head comprises shield layers 202, 204, MR sensor 203, shaping layer 210, coil structure 208, main pole 212, lower return pole layer 206, wrap around shield 214, and upper return pole layer 216. Alternatively, structure 214 may also be a trailing shield. Shield layer 202 is supported by undercoat layer 218 and an AlTiC base layer 220. Details of wrap around shields and trailing shields, as applied to perpendicular recording heads, can be found in, for example, US Patent Application Publications 2007/0146930, 2007/0115584, 2006/0174474, 2006/0044682, and 2007/0137027.
FIG. 3 (Prior Art) is a partial cross sectional view 300 of a thin film longitudinal head undergoing thermal expansion during thermal fly height control. Thermal fly height control engages the use of heaters embedded within the thin film head structure (not shown) to cause distortion of the air bearing surface (ABS) when the head is heated. Thermal expansion of materials within the head cause the dynamic position of the ABS to move toward the disk surface. This alters the effective fly height of the head over the media disk surface. In FIG. 3, the dashed line marked ABSc indicates the position of the air bearing surface in an unheated condition (as in FIG. 1). The dashed line marked ABSh indicates the distorted position of the air bearing surface subsequent to heating. Unfortunately, the distortion produced by the thermal fly height control heaters make critical components such as shield layers 101, 102; sensor 103; pole tips 110, 108; and lower pole layer 106 more susceptible to damage by electrostatic discharge from the media disk surface.
FIG. 4 (Prior Art) is a partial, cross sectional view 400 of a thin film perpendicular head undergoing thermal expansion during thermal fly height control. As was discussed with the longitudinal head of FIG. 3, distortion produced by the thermal fly height control heaters make critical components more susceptible to damage by electrostatic discharge from the media disk surface in this design as well.